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        </div><article class="page single"><h1 class="single-title animated flipInX">Spring源码 - DispatcherServlet 处理请求的核心流程</h1><div class="post-meta">
            <div class="post-meta-line"><span class="post-author"><a href="https://wlizhi.cc" title="Author" target="_blank" rel="noopener noreffer author" class="author"><i class="fas fa-user-circle fa-fw"></i>Wlizhi</a></span>&nbsp;<span class="post-category">收录于 <a href="/categories/spring/"><i class="far fa-folder fa-fw"></i>spring</a></span></div>
            <div class="post-meta-line"><i class="far fa-calendar-alt fa-fw"></i>&nbsp;<time datetime="2020-12-16">2020-12-16</time>&nbsp;<i class="fas fa-pencil-alt fa-fw"></i>&nbsp;约 6315 字&nbsp;
                <i class="far fa-clock fa-fw"></i>&nbsp;预计阅读 13 分钟&nbsp;<span id="/posts/spring/26-dispatcher-servlet-core-process/" class="leancloud_visitors" data-flag-title="Spring源码 - DispatcherServlet 处理请求的核心流程">
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  <ul>
    <li><a href="#1-处理请求的入口">1 处理请求的入口</a></li>
    <li><a href="#2-gethandler-获取handlermethod及拦截器的封装类">2 getHandler() 获取handlerMethod及拦截器的封装类</a>
      <ul>
        <li><a href="#21-gethandlerinternal">2.1 getHandlerInternal()</a></li>
        <li><a href="#22-gethandlerexecutionchain">2.2 getHandlerExecutionChain()</a></li>
      </ul>
    </li>
    <li><a href="#3-gethandleradapter">3 getHandlerAdapter()</a></li>
    <li><a href="#4-前置拦截---applyprehandle">4 前置拦截 - applyPreHandle()</a></li>
    <li><a href="#5-中置拦截---applyposthandle">5 中置拦截 - applyPostHandle()</a></li>
    <li><a href="#6-全局异常处理及后置拦截---processdispatchresult">6 全局异常处理及后置拦截 - processDispatchResult()</a></li>
  </ul>
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            </div><div class="content" id="content"><p>spring源码系列文章，示例代码的中文注释，均是 copy 自 <a href="https://gitee.com/wlizhi/spring-framework" target="_blank" rel="noopener noreffer">https://gitee.com/wlizhi/spring-framework</a> 。</p>
<p>链接中源码是作者从 github 下载，并以自身理解对核心流程及主要节点做了详细的中文注释。</p>
<hr>
<h2 id="1-处理请求的入口">1 处理请求的入口</h2>
<p>根据 servlet 规范，当服务器在接收到请求时，会调用至 servlet.service() 方法，进行处理，DispatcherServlet 就是如此。</p>
<p>例如一个post请求，会经过以下调用：</p>
<blockquote>
<p>service() -&gt; doPost() -&gt; processRequest() -&gt; doService() -&gt; doDispatch()</p>
</blockquote>
<p>无论什么类型的请求，最终都会调用至 doDispatch()。</p>
<p>doDispatch() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DispatcherServlet</span> <span class="kd">extends</span> <span class="n">FrameworkServlet</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl"><span class="kd">protected</span> <span class="kt">void</span> <span class="nf">doDispatch</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">,</span> <span class="n">HttpServletResponse</span> <span class="n">response</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">HttpServletRequest</span> <span class="n">processedRequest</span> <span class="o">=</span> <span class="n">request</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="n">HandlerExecutionChain</span> <span class="n">mappedHandler</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="kt">boolean</span> <span class="n">multipartRequestParsed</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="cm">/* TODO
</span></span></span><span class="line"><span class="cl"><span class="cm">		    预处理：
</span></span></span><span class="line"><span class="cl"><span class="cm">		        1. 获取HandlerMethod和过滤器链的包装类（url-hanlderMethod映射）：HandlerExecutionChain，里面包含了handlerMethod对象
</span></span></span><span class="line"><span class="cl"><span class="cm">		        2. 根据handlerMethod对象，找到合适的HandlerAdapter对象，这里用到了策略模式
</span></span></span><span class="line"><span class="cl"><span class="cm">		    调用链：
</span></span></span><span class="line"><span class="cl"><span class="cm">		        1. 前置拦截，正向遍历调用，若有返回false，则调用后置处理，返回。
</span></span></span><span class="line"><span class="cl"><span class="cm">				    interceptor.preHandle(request, response, this.handler)
</span></span></span><span class="line"><span class="cl"><span class="cm">				    triggerAfterCompletion(request, response, null);
</span></span></span><span class="line"><span class="cl"><span class="cm">			    2. 根据HandlerAdapter获取真正的处理类，执行：((Controller) handler).handleRequest(request, response)
</span></span></span><span class="line"><span class="cl"><span class="cm">			    3. 中置拦截，反向遍历调用。 interceptor.postHandle(request, response, this.handler, mv);
</span></span></span><span class="line"><span class="cl"><span class="cm">			    4. 视图渲染，在视图渲染之后，会在视图渲染方法中调用后置处理。
</span></span></span><span class="line"><span class="cl"><span class="cm">			        render(mv, request, response);
</span></span></span><span class="line"><span class="cl"><span class="cm">			        if (mappedHandler != null) {
</span></span></span><span class="line"><span class="cl"><span class="cm">						mappedHandler.triggerAfterCompletion(request, response, null);
</span></span></span><span class="line"><span class="cl"><span class="cm">				    }
</span></span></span><span class="line"><span class="cl"><span class="cm">			*/</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 异步管理
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">WebAsyncManager</span> <span class="n">asyncManager</span> <span class="o">=</span> <span class="n">WebAsyncUtils</span><span class="o">.</span><span class="na">getAsyncManager</span><span class="o">(</span><span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">ModelAndView</span> <span class="n">mv</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="n">Exception</span> <span class="n">dispatchException</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">			<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 文件上传
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">processedRequest</span> <span class="o">=</span> <span class="n">checkMultipart</span><span class="o">(</span><span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">multipartRequestParsed</span> <span class="o">=</span> <span class="o">(</span><span class="n">processedRequest</span> <span class="o">!=</span> <span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 这个方法很重要，重点看 获取封装了 handlerMethod、拦截器的执行链封装 HandlerExecutionChain。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// Determine handler for the current request.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">mappedHandler</span> <span class="o">=</span> <span class="n">getHandler</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">mappedHandler</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">noHandlerFound</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 获取跟HandlerMethod匹配的HandlerAdapter对象
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// Determine handler adapter for the current request.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">HandlerAdapter</span> <span class="n">ha</span> <span class="o">=</span> <span class="n">getHandlerAdapter</span><span class="o">(</span><span class="n">mappedHandler</span><span class="o">.</span><span class="na">getHandler</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// Process last-modified header, if supported by the handler.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">String</span> <span class="n">method</span> <span class="o">=</span> <span class="n">request</span><span class="o">.</span><span class="na">getMethod</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="kt">boolean</span> <span class="n">isGet</span> <span class="o">=</span> <span class="s">&#34;GET&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">isGet</span> <span class="o">||</span> <span class="s">&#34;HEAD&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">method</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="kt">long</span> <span class="n">lastModified</span> <span class="o">=</span> <span class="n">ha</span><span class="o">.</span><span class="na">getLastModified</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">mappedHandler</span><span class="o">.</span><span class="na">getHandler</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">					<span class="k">if</span> <span class="o">(</span><span class="k">new</span> <span class="n">ServletWebRequest</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">).</span><span class="na">checkNotModified</span><span class="o">(</span><span class="n">lastModified</span><span class="o">)</span> <span class="o">&amp;&amp;</span> <span class="n">isGet</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="k">return</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 前置过滤器，如果为false则直接返回
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(!</span><span class="n">mappedHandler</span><span class="o">.</span><span class="na">applyPreHandle</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 调用到Controller具体方法，核心方法调用，重点看看
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// Actually invoke the handler.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">mv</span> <span class="o">=</span> <span class="n">ha</span><span class="o">.</span><span class="na">handle</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="n">mappedHandler</span><span class="o">.</span><span class="na">getHandler</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">asyncManager</span><span class="o">.</span><span class="na">isConcurrentHandlingStarted</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="n">applyDefaultViewName</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">mv</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 执行中置拦截
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">mappedHandler</span><span class="o">.</span><span class="na">applyPostHandle</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="n">mv</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">dispatchException</span> <span class="o">=</span> <span class="n">ex</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">err</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// As of 4.3, we&#39;re processing Errors thrown from handler methods as well,
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// making them available for @ExceptionHandler methods and other scenarios.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">dispatchException</span> <span class="o">=</span> <span class="k">new</span> <span class="n">NestedServletException</span><span class="o">(</span><span class="s">&#34;Handler dispatch failed&#34;</span><span class="o">,</span> <span class="n">err</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// TODO 处理结果，这里执行了后置拦截。在前面的流程里捕获了业务方法执行过程中抛出的异常。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="c1">//  如果上面的流程中抛出了异常，则dispatchException一定有值。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">processDispatchResult</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="n">mappedHandler</span><span class="o">,</span> <span class="n">mv</span><span class="o">,</span> <span class="n">dispatchException</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">triggerAfterCompletion</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="n">mappedHandler</span><span class="o">,</span> <span class="n">ex</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">err</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">triggerAfterCompletion</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="n">mappedHandler</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">					<span class="k">new</span> <span class="n">NestedServletException</span><span class="o">(</span><span class="s">&#34;Handler processing failed&#34;</span><span class="o">,</span> <span class="n">err</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">finally</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">asyncManager</span><span class="o">.</span><span class="na">isConcurrentHandlingStarted</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// Instead of postHandle and afterCompletion
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">mappedHandler</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">mappedHandler</span><span class="o">.</span><span class="na">applyAfterConcurrentHandlingStarted</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">,</span> <span class="n">response</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// Clean up any resources used by a multipart request.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">multipartRequestParsed</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">cleanupMultipart</span><span class="o">(</span><span class="n">processedRequest</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>主要调用流程如下：</p>
<ol>
<li>获取到 HandlerExecutionChain。其中封装了 handlerMethod 和 拦截器链。</li>
<li>获取 HandlerAdapter。</li>
<li>调用拦截器前置拦截方法 preHandle()。</li>
<li>调用 handle()，内部通过反射调用了controller中的业务方法。</li>
<li>调用 applyPostHandle()，执行中置拦截。</li>
<li>调用 processDispatchResult()，内部调用了全局异常处理和后置拦截。</li>
</ol>
<p>前面五个步骤是在 try catch 块中执行的，如果执行中发生了异常，会被捕获到，变量 dispatchException 也就有值了，这时候才会触发全局异常处理。</p>
<h2 id="2-gethandler-获取handlermethod及拦截器的封装类">2 getHandler() 获取handlerMethod及拦截器的封装类</h2>
<p>getHandler() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DispatcherServlet</span> <span class="kd">extends</span> <span class="n">FrameworkServlet</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">HandlerExecutionChain</span> <span class="nf">getHandler</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// handlerMappering实例
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">handlerMappings</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 在 DispatcherServlet 初始化的时候，会将handlerMappings的值，赋值到这里。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">for</span> <span class="o">(</span><span class="n">HandlerMapping</span> <span class="n">mapping</span> <span class="o">:</span> <span class="k">this</span><span class="o">.</span><span class="na">handlerMappings</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 获取HandlerMethod和拦截器链的包装类
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">HandlerExecutionChain</span> <span class="n">handler</span> <span class="o">=</span> <span class="n">mapping</span><span class="o">.</span><span class="na">getHandler</span><span class="o">(</span><span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">handler</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span> <span class="n">handler</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>遍历 handlerMappings，依次调用 getHandler()，如果获取到执行链，就返回。</p>
<p>getHandler() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractHandlerMapping</span> <span class="kd">extends</span> <span class="n">WebApplicationObjectSupport</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">HandlerMapping</span><span class="o">,</span> <span class="n">Ordered</span><span class="o">,</span> <span class="n">BeanNameAware</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kd">final</span> <span class="n">HandlerExecutionChain</span> <span class="nf">getHandler</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 获取 HandlerMethod
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Object</span> <span class="n">handler</span> <span class="o">=</span> <span class="n">getHandlerInternal</span><span class="o">(</span><span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">handler</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">handler</span> <span class="o">=</span> <span class="n">getDefaultHandler</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">handler</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// Bean name or resolved handler?
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">handler</span> <span class="k">instanceof</span> <span class="n">String</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">String</span> <span class="n">handlerName</span> <span class="o">=</span> <span class="o">(</span><span class="n">String</span><span class="o">)</span> <span class="n">handler</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="n">handler</span> <span class="o">=</span> <span class="n">obtainApplicationContext</span><span class="o">().</span><span class="na">getBean</span><span class="o">(</span><span class="n">handlerName</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 将 handlerMethod，包装到 HandlerExecutionChain 中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">HandlerExecutionChain</span> <span class="n">executionChain</span> <span class="o">=</span> <span class="n">getHandlerExecutionChain</span><span class="o">(</span><span class="n">handler</span><span class="o">,</span> <span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略无关代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="n">executionChain</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>这里有两个关键的方法调用，getHandlerInternal()、getHandlerExecutionChain()。</p>
<h3 id="21-gethandlerinternal">2.1 getHandlerInternal()</h3>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractHandlerMethodMapping</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span> <span class="kd">extends</span> <span class="n">AbstractHandlerMapping</span> <span class="kd">implements</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">HandlerMethod</span> <span class="nf">getHandlerInternal</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">String</span> <span class="n">lookupPath</span> <span class="o">=</span> <span class="n">getUrlPathHelper</span><span class="o">().</span><span class="na">getLookupPathForRequest</span><span class="o">(</span><span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="k">this</span><span class="o">.</span><span class="na">mappingRegistry</span><span class="o">.</span><span class="na">acquireReadLock</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 根据路径获取到 HandlerMapping，再根据 HandlerMapping 获取到 HandlerMethod
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">HandlerMethod</span> <span class="n">handlerMethod</span> <span class="o">=</span> <span class="n">lookupHandlerMethod</span><span class="o">(</span><span class="n">lookupPath</span><span class="o">,</span> <span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// TODO 因为在初始化 HandlerMethod 时，并没有将bean实例封装进去，只是封装了一个 beanClass 和 beanName。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="c1">//  如果获取到 handlerMethod 不为空，则会在这里进行 getBean 操作，将 bean 实例封装到 handlerMethod中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">return</span> <span class="o">(</span><span class="n">handlerMethod</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">?</span> <span class="n">handlerMethod</span><span class="o">.</span><span class="na">createWithResolvedBean</span><span class="o">()</span> <span class="o">:</span> <span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">finally</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">this</span><span class="o">.</span><span class="na">mappingRegistry</span><span class="o">.</span><span class="na">releaseReadLock</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>首先根据请求路径，获取到 HandlerMethod。如果 HandlerMethod 存在，则将内部封装的 beanName，通过调用 getBean()，获取到具体的实例，
将获取到的实例缓存到成员变量中，替换掉变量 beanName。</p>
<hr>
<p>lookupHandlerMethod() 中，会首先通过 url 获取到 HandlerMappingInfo，再通过 HandlerMappingInfo 获取到具体的 handlerMethod。</p>
<p>lookupHandlerMethod中的部分源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractHandlerMethodMapping</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span> <span class="kd">extends</span> <span class="n">AbstractHandlerMapping</span> <span class="kd">implements</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">HandlerMethod</span> <span class="nf">lookupHandlerMethod</span><span class="o">(</span><span class="n">String</span> <span class="n">lookupPath</span><span class="o">,</span> <span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">List</span><span class="o">&lt;</span><span class="n">Match</span><span class="o">&gt;</span> <span class="n">matches</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 根据url路径从 urlLookup 中获取 RequestMappingInfo
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">List</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span> <span class="n">directPathMatches</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">mappingRegistry</span><span class="o">.</span><span class="na">getMappingsByUrl</span><span class="o">(</span><span class="n">lookupPath</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">directPathMatches</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">addMatchingMappings</span><span class="o">(</span><span class="n">directPathMatches</span><span class="o">,</span> <span class="n">matches</span><span class="o">,</span> <span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(!</span><span class="n">matches</span><span class="o">.</span><span class="na">isEmpty</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 获取最佳匹配，代码省略...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">return</span> <span class="n">bestMatch</span><span class="o">.</span><span class="na">handlerMethod</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span> <span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>如以上源码，在 getMappingsByUrl() 中就获取了 RequestMappingInfo 实例列表。是从成员变量 urlLookup 中获取的。</p>
<p>addMatchingMappings() 中，从成员变来那个 mappingLookup 获取到了 handlerMethod。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractHandlerMethodMapping</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span> <span class="kd">extends</span> <span class="n">AbstractHandlerMapping</span> <span class="kd">implements</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kt">void</span> <span class="nf">addMatchingMappings</span><span class="o">(</span><span class="n">Collection</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span> <span class="n">mappings</span><span class="o">,</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">Match</span><span class="o">&gt;</span> <span class="n">matches</span><span class="o">,</span> <span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">for</span> <span class="o">(</span><span class="n">T</span> <span class="n">mapping</span> <span class="o">:</span> <span class="n">mappings</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">T</span> <span class="n">match</span> <span class="o">=</span> <span class="n">getMatchingMapping</span><span class="o">(</span><span class="n">mapping</span><span class="o">,</span> <span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">match</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 从 mappingLookup 中获取 handlerMethod
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">matches</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">Match</span><span class="o">(</span><span class="n">match</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">mappingRegistry</span><span class="o">.</span><span class="na">getMappings</span><span class="o">().</span><span class="na">get</span><span class="o">(</span><span class="n">mapping</span><span class="o">)));</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">Map</span><span class="o">&lt;</span><span class="n">T</span><span class="o">,</span> <span class="n">HandlerMethod</span><span class="o">&gt;</span> <span class="nf">getMappings</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">return</span> <span class="k">this</span><span class="o">.</span><span class="na">mappingLookup</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>上面代码中，注意 getMappings() 方法返回的是 this.mappingLookup，这是一个 map 集合，封装了 RequestMappingInfo - HandlerMethod 的映射关系。</p>
<hr>
<p>createWithResolvedBean() 源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerMethod</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">HandlerMethod</span> <span class="nf">createWithResolvedBean</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">Object</span> <span class="n">handler</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">bean</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 最初这个 bean 成员变量，只是设置了一个 beanName，因此它是字符串类型的，执行到这里会调用 getBean()，将真正的实例设置到这里。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 如果已经设置过了，bean就不是字符串类型了，就不会进这个 if 语句。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">bean</span> <span class="k">instanceof</span> <span class="n">String</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">Assert</span><span class="o">.</span><span class="na">state</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">beanFactory</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">,</span> <span class="s">&#34;Cannot resolve bean name without BeanFactory&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="n">String</span> <span class="n">beanName</span> <span class="o">=</span> <span class="o">(</span><span class="n">String</span><span class="o">)</span> <span class="k">this</span><span class="o">.</span><span class="na">bean</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="n">handler</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">beanFactory</span><span class="o">.</span><span class="na">getBean</span><span class="o">(</span><span class="n">beanName</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="k">new</span> <span class="n">HandlerMethod</span><span class="o">(</span><span class="k">this</span><span class="o">,</span> <span class="n">handler</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>前文中有提到，在 RequestMappingHandlerMapping 初始化的时候，是收集了HandlerMethod的，而在封装 HandlerMethod 时，并没有设置具体的 bean 实例，仅仅设置了 beanClass 以及 beanName。bean 的实例就是在这里进行设置的。</p>
<p>如上源码，当容器启动后，第一个请求进来时，this.bean 中存储的是 beanName，也就是一个字符串。这时候就会触发调用 getBean()，将 this.bean 的值替换为 bean 的实例对象。</p>
<p>后面再有请求过来，就不会再调用 getBean 了。这里的 new HandlerMethod()，类似于一种copy。因为在执行过程中，可能会修改内部封装的一些属性值，即每一个线程获取到的这个对象要是线程安全的（或者说是线程独立的），所以才要重新创建一个 HandlerMethod 实例。</p>
<h3 id="22-gethandlerexecutionchain">2.2 getHandlerExecutionChain()</h3>
<p>getHandlerExecutionChain() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractHandlerMapping</span> <span class="kd">extends</span> <span class="n">WebApplicationObjectSupport</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">HandlerMapping</span><span class="o">,</span> <span class="n">Ordered</span><span class="o">,</span> <span class="n">BeanNameAware</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="n">HandlerExecutionChain</span> <span class="nf">getHandlerExecutionChain</span><span class="o">(</span><span class="n">Object</span> <span class="n">handler</span><span class="o">,</span> <span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 创建拦截器链
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">HandlerExecutionChain</span> <span class="n">chain</span> <span class="o">=</span> <span class="o">(</span><span class="n">handler</span> <span class="k">instanceof</span> <span class="n">HandlerExecutionChain</span> <span class="o">?</span>
</span></span><span class="line"><span class="cl">				<span class="o">(</span><span class="n">HandlerExecutionChain</span><span class="o">)</span> <span class="n">handler</span> <span class="o">:</span> <span class="k">new</span> <span class="n">HandlerExecutionChain</span><span class="o">(</span><span class="n">handler</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 拦截器匹配，获取拦截器执行链
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">String</span> <span class="n">lookupPath</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">urlPathHelper</span><span class="o">.</span><span class="na">getLookupPathForRequest</span><span class="o">(</span><span class="n">request</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 遍历所有的拦截器，如果是 MappedInterceptor，根据拦截器的 excludePatterns 和 includePatterns 来进行匹配。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 如果没有配置 includePatterns 且在 excludePatterns 没有匹配到，则默认为 true。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 也就是说 MappedInterceptor 中具有路径匹配功能，同时包装了一个 HandlerInterceptor 实现。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 而 HandlerInterceptor 中仅仅定义了 前置、中置、后置拦截方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">for</span> <span class="o">(</span><span class="n">HandlerInterceptor</span> <span class="n">interceptor</span> <span class="o">:</span> <span class="k">this</span><span class="o">.</span><span class="na">adaptedInterceptors</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">interceptor</span> <span class="k">instanceof</span> <span class="n">MappedInterceptor</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">MappedInterceptor</span> <span class="n">mappedInterceptor</span> <span class="o">=</span> <span class="o">(</span><span class="n">MappedInterceptor</span><span class="o">)</span> <span class="n">interceptor</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">mappedInterceptor</span><span class="o">.</span><span class="na">matches</span><span class="o">(</span><span class="n">lookupPath</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">pathMatcher</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">chain</span><span class="o">.</span><span class="na">addInterceptor</span><span class="o">(</span><span class="n">mappedInterceptor</span><span class="o">.</span><span class="na">getInterceptor</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">chain</span><span class="o">.</span><span class="na">addInterceptor</span><span class="o">(</span><span class="n">interceptor</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">chain</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>首先创建 HandlerExecutionChain，将 HandlerMethod 封装。
遍历所有的拦截器，如果拦截器是 MappedInterceptor 类型，则调用 matches() 进行路径匹配，匹配为 true，就加入到拦截器执行链中。这里的拦截器链就是一个 List。</p>
<p>HandlerExecutionChain 的数据结构：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerExecutionChain</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">Log</span> <span class="n">logger</span> <span class="o">=</span> <span class="n">LogFactory</span><span class="o">.</span><span class="na">getLog</span><span class="o">(</span><span class="n">HandlerExecutionChain</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="cm">/** 这里是一个 handlerMethod */</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">final</span> <span class="n">Object</span> <span class="n">handler</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="cm">/** 拦截器 最终会合并到 interceptorList */</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Nullable</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="n">HandlerInterceptor</span><span class="o">[]</span> <span class="n">interceptors</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">    <span class="cm">/** 拦截器 */</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Nullable</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">HandlerInterceptor</span><span class="o">&gt;</span> <span class="n">interceptorList</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kt">int</span> <span class="n">interceptorIndex</span> <span class="o">=</span> <span class="o">-</span><span class="n">1</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">addInterceptor</span><span class="o">(</span><span class="n">HandlerInterceptor</span> <span class="n">interceptor</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">initInterceptorList</span><span class="o">().</span><span class="na">add</span><span class="o">(</span><span class="n">interceptor</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">HandlerInterceptor</span><span class="o">&gt;</span> <span class="nf">initInterceptorList</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">interceptorList</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">this</span><span class="o">.</span><span class="na">interceptorList</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 如果 interceptors 中有值，合并到 interceptorList 中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">interceptors</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// An interceptor array specified through the constructor
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">CollectionUtils</span><span class="o">.</span><span class="na">mergeArrayIntoCollection</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">interceptors</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">interceptorList</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">this</span><span class="o">.</span><span class="na">interceptors</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="k">this</span><span class="o">.</span><span class="na">interceptorList</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>从其数据结构中可以看出，内部就是封装了 handler 和多个拦截器组成的 interceptorList 列表。</p>
<p>在添加拦截器时，会调用 initInterceptorList()，如果 interceptors 中有值，会合并到列表中。</p>
<p>如此，就将 HandlerMethod 以及匹配的拦截器封装为 HandlerExecutionChain 返回了。</p>
<h2 id="3-gethandleradapter">3 getHandlerAdapter()</h2>
<p>这里是典型的策略模式，从 handlerAdapters 中遍历，依次调用 supports() 判断是否支持当前的 handlerMethod，如果支持，就返回。如果最终未找到有支持的 HandlerAdapter，会抛出异常。</p>
<p>这也是为什么在初始化的时候，会默认注册那么多 HandlerAdapter 的原因。spring 考虑到了大多数的一些 参数、返回值 等的处理策略。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DispatcherServlet</span> <span class="kd">extends</span> <span class="n">FrameworkServlet</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">HandlerAdapter</span> <span class="nf">getHandlerAdapter</span><span class="o">(</span><span class="n">Object</span> <span class="n">handler</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ServletException</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 根据handlerMethod对象，找到合适的HandlerAdapter对象，这里是典型的的策略模式
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 遍历所有的 handlerAdapters，并调用其 supports()，如果有 adapter 支持这个 handlerMethod，就返回这个 adapter。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">handlerAdapters</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="n">HandlerAdapter</span> <span class="n">adapter</span> <span class="o">:</span> <span class="k">this</span><span class="o">.</span><span class="na">handlerAdapters</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">adapter</span><span class="o">.</span><span class="na">supports</span><span class="o">(</span><span class="n">handler</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span> <span class="n">adapter</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">throw</span> <span class="k">new</span> <span class="n">ServletException</span><span class="o">(</span><span class="s">&#34;No adapter for handler [&#34;</span> <span class="o">+</span> <span class="n">handler</span> <span class="o">+</span>
</span></span><span class="line"><span class="cl">				<span class="s">&#34;]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="4-前置拦截---applyprehandle">4 前置拦截 - applyPreHandle()</h2>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerExecutionChain</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kt">boolean</span> <span class="nf">applyPreHandle</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">,</span> <span class="n">HttpServletResponse</span> <span class="n">response</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">HandlerInterceptor</span><span class="o">[]</span> <span class="n">interceptors</span> <span class="o">=</span> <span class="n">getInterceptors</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(!</span><span class="n">ObjectUtils</span><span class="o">.</span><span class="na">isEmpty</span><span class="o">(</span><span class="n">interceptors</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="n">0</span><span class="o">;</span> <span class="n">i</span> <span class="o">&lt;</span> <span class="n">interceptors</span><span class="o">.</span><span class="na">length</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">HandlerInterceptor</span> <span class="n">interceptor</span> <span class="o">=</span> <span class="n">interceptors</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 遍历执行拦截器的前置方法，只要有一个返回了false，就返回false。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 每次执行一个前置拦截后，就将interceptorIndex+1，当有前置方法返回false时，执行triggerAfterCompletion。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(!</span><span class="n">interceptor</span><span class="o">.</span><span class="na">preHandle</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">handler</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// 倒序执行后置拦截，起始索引是 interceptorIndex，即如果也有前置拦截执行失败了，
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="c1">// 那么相应的这个失败的及之后的拦截器的后置拦截就不会执行。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="n">triggerAfterCompletion</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="k">this</span><span class="o">.</span><span class="na">interceptorIndex</span> <span class="o">=</span> <span class="n">i</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>调用执行链中的方法，遍历执行拦截器的前置拦截方法，每成功执行一个，将成员变量 interceptorIndex 的值 +1，在这之间如果前置拦截返回 false，就会跳过中置拦截，直接触发后置拦截。</p>
<p>也就是说，如果有任何一个前置拦截返回了 false，那么所有的中置拦截方法都不会执行。</p>
<p>后置拦截的执行时倒序的，并不一定是从最后一个开始，而是根据最后一个返回 true 的前置拦截的索引 interceptorIndex 开始，倒序执行到列表的开头。</p>
<p>后置拦截的源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerExecutionChain</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kt">void</span> <span class="nf">triggerAfterCompletion</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">,</span> <span class="n">HttpServletResponse</span> <span class="n">response</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">Exception</span> <span class="n">ex</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">			<span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="n">HandlerInterceptor</span><span class="o">[]</span> <span class="n">interceptors</span> <span class="o">=</span> <span class="n">getInterceptors</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(!</span><span class="n">ObjectUtils</span><span class="o">.</span><span class="na">isEmpty</span><span class="o">(</span><span class="n">interceptors</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 倒序执行，起始索引是最后一个返回 true 的前置拦截的索引。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">interceptorIndex</span><span class="o">;</span> <span class="n">i</span> <span class="o">&gt;=</span> <span class="n">0</span><span class="o">;</span> <span class="n">i</span><span class="o">--)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">HandlerInterceptor</span> <span class="n">interceptor</span> <span class="o">=</span> <span class="n">interceptors</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
</span></span><span class="line"><span class="cl">				<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">interceptor</span><span class="o">.</span><span class="na">afterCompletion</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">handler</span><span class="o">,</span> <span class="n">ex</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">ex2</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">logger</span><span class="o">.</span><span class="na">error</span><span class="o">(</span><span class="s">&#34;HandlerInterceptor.afterCompletion threw exception&#34;</span><span class="o">,</span> <span class="n">ex2</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="5-中置拦截---applyposthandle">5 中置拦截 - applyPostHandle()</h2>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerExecutionChain</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kt">void</span> <span class="nf">applyPostHandle</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">,</span> <span class="n">HttpServletResponse</span> <span class="n">response</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">ModelAndView</span> <span class="n">mv</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">			<span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="n">HandlerInterceptor</span><span class="o">[]</span> <span class="n">interceptors</span> <span class="o">=</span> <span class="n">getInterceptors</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(!</span><span class="n">ObjectUtils</span><span class="o">.</span><span class="na">isEmpty</span><span class="o">(</span><span class="n">interceptors</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 如果存在拦截器，倒序执行中置拦截。能执行到这个方法，说明所有的前置拦截都成功执行了。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="n">interceptors</span><span class="o">.</span><span class="na">length</span> <span class="o">-</span> <span class="n">1</span><span class="o">;</span> <span class="n">i</span> <span class="o">&gt;=</span> <span class="n">0</span><span class="o">;</span> <span class="n">i</span><span class="o">--)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">HandlerInterceptor</span> <span class="n">interceptor</span> <span class="o">=</span> <span class="n">interceptors</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
</span></span><span class="line"><span class="cl">				<span class="n">interceptor</span><span class="o">.</span><span class="na">postHandle</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">handler</span><span class="o">,</span> <span class="n">mv</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>中置拦截是从最后一个索引开始，倒序执行的。能执行到这里，那么所有的前置拦截一定全部返回了true。所以这里可以不用根据前面记录的索引来执行，而是直接从最后一个索引开始，倒序执行。</p>
<h2 id="6-全局异常处理及后置拦截---processdispatchresult">6 全局异常处理及后置拦截 - processDispatchResult()</h2>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DispatcherServlet</span> <span class="kd">extends</span> <span class="n">FrameworkServlet</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="kt">void</span> <span class="nf">processDispatchResult</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">,</span> <span class="n">HttpServletResponse</span> <span class="n">response</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="nd">@Nullable</span> <span class="n">HandlerExecutionChain</span> <span class="n">mappedHandler</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">ModelAndView</span> <span class="n">mv</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="nd">@Nullable</span> <span class="n">Exception</span> <span class="n">exception</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="kt">boolean</span> <span class="n">errorView</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 如果前面的流程中抛出了异常，在这里会进行处理。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">exception</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">exception</span> <span class="k">instanceof</span> <span class="n">ModelAndViewDefiningException</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;ModelAndViewDefiningException encountered&#34;</span><span class="o">,</span> <span class="n">exception</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">mv</span> <span class="o">=</span> <span class="o">((</span><span class="n">ModelAndViewDefiningException</span><span class="o">)</span> <span class="n">exception</span><span class="o">).</span><span class="na">getModelAndView</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 异常处理
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">Object</span> <span class="n">handler</span> <span class="o">=</span> <span class="o">(</span><span class="n">mappedHandler</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">?</span> <span class="n">mappedHandler</span><span class="o">.</span><span class="na">getHandler</span><span class="o">()</span> <span class="o">:</span> <span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">mv</span> <span class="o">=</span> <span class="n">processHandlerException</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="n">handler</span><span class="o">,</span> <span class="n">exception</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">errorView</span> <span class="o">=</span> <span class="o">(</span><span class="n">mv</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">mappedHandler</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 执行后置拦截
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">mappedHandler</span><span class="o">.</span><span class="na">triggerAfterCompletion</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">response</span><span class="o">,</span> <span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>在外围方法中，是捕获了具体方法执行过程中，抛出的异常的。</p>
<p>如果业务方法中抛出了异常，则会作为参数传递到这里。如果存在异常，就会调用全局异常处理。</p>
<p>最后执行后置拦截。</p>
<p>异常处理也是通过策略模式实现，在接口 HandlerExceptionResolver 中，只定义了 resolveException()，而在其抽象子类中定义了 shouldApplyTo()，这个方法判断了当前的异常处理类是否支持指定的异常。</p>
<p>遍历所有的异常处理实例，首先判断是否支持，如果支持处理当前异常，就会调用 doResolveHandlerMethodException()。</p>
<p>doResolveHandlerMethodException() 大体分为两步，首先获取异常处理方法对象，然后执行异常处理方法。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ExceptionHandlerExceptionResolver</span> <span class="kd">extends</span> <span class="n">AbstractHandlerMethodExceptionResolver</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">ApplicationContextAware</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">ModelAndView</span> <span class="nf">doResolveHandlerMethodException</span><span class="o">(</span><span class="n">HttpServletRequest</span> <span class="n">request</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="n">HttpServletResponse</span> <span class="n">response</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">HandlerMethod</span> <span class="n">handlerMethod</span><span class="o">,</span> <span class="n">Exception</span> <span class="n">exception</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 获取异常处理方法
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">ServletInvocableHandlerMethod</span> <span class="n">exceptionHandlerMethod</span> <span class="o">=</span> <span class="n">getExceptionHandlerMethod</span><span class="o">(</span><span class="n">handlerMethod</span><span class="o">,</span> <span class="n">exception</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">exceptionHandlerMethod</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 设置参数解析器和返回值处理器
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">argumentResolvers</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">exceptionHandlerMethod</span><span class="o">.</span><span class="na">setHandlerMethodArgumentResolvers</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">argumentResolvers</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">returnValueHandlers</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">exceptionHandlerMethod</span><span class="o">.</span><span class="na">setHandlerMethodReturnValueHandlers</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">returnValueHandlers</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="n">Throwable</span> <span class="n">cause</span> <span class="o">=</span> <span class="n">exception</span><span class="o">.</span><span class="na">getCause</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">cause</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="c1">// 异常处理方法的执行。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>            <span class="c1">// Expose cause as provided argument as well
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>            <span class="n">exceptionHandlerMethod</span><span class="o">.</span><span class="na">invokeAndHandle</span><span class="o">(</span><span class="n">webRequest</span><span class="o">,</span> <span class="n">mavContainer</span><span class="o">,</span> <span class="n">exception</span><span class="o">,</span> <span class="n">cause</span><span class="o">,</span> <span class="n">handlerMethod</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>ServletInvocableHandlerMethod 的获取源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ExceptionHandlerExceptionResolver</span> <span class="kd">extends</span> <span class="n">AbstractHandlerMethodExceptionResolver</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">ApplicationContextAware</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">ServletInvocableHandlerMethod</span> <span class="nf">getExceptionHandlerMethod</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">			<span class="nd">@Nullable</span> <span class="n">HandlerMethod</span> <span class="n">handlerMethod</span><span class="o">,</span> <span class="n">Exception</span> <span class="n">exception</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="n">Class</span><span class="o">&lt;?&gt;</span> <span class="n">handlerType</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 获取异常处理方法，这里使用了缓存，也就是只会查找一次。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">handlerMethod</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// Local exception handler methods on the controller class itself.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="c1">// To be invoked through the proxy, even in case of an interface-based proxy.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">handlerType</span> <span class="o">=</span> <span class="n">handlerMethod</span><span class="o">.</span><span class="na">getBeanType</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">			<span class="n">ExceptionHandlerMethodResolver</span> <span class="n">resolver</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">exceptionHandlerCache</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">handlerType</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">resolver</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// ExceptionHandlerMethodResolver定义了对注解@ExceptionHandler的支持
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 查找@ControllerAdvice标注的处理类中，标注有 @ExceptionHandler 的方法，并将注解中配置的 Exception类型与方法的反射对象
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 映射关系封装缓存起来。如果一个controller中抛出了异常，就可以根据这个异常从异常处理类中找到这个处理方法了。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">resolver</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ExceptionHandlerMethodResolver</span><span class="o">(</span><span class="n">handlerType</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">this</span><span class="o">.</span><span class="na">exceptionHandlerCache</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">handlerType</span><span class="o">,</span> <span class="n">resolver</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="n">Method</span> <span class="n">method</span> <span class="o">=</span> <span class="n">resolver</span><span class="o">.</span><span class="na">resolveMethod</span><span class="o">(</span><span class="n">exception</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">method</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="k">new</span> <span class="n">ServletInvocableHandlerMethod</span><span class="o">(</span><span class="n">handlerMethod</span><span class="o">.</span><span class="na">getBean</span><span class="o">(),</span> <span class="n">method</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// For advice applicability check below (involving base packages, assignable types
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="c1">// and annotation presence), use target class instead of interface-based proxy.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="n">Proxy</span><span class="o">.</span><span class="na">isProxyClass</span><span class="o">(</span><span class="n">handlerType</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">handlerType</span> <span class="o">=</span> <span class="n">AopUtils</span><span class="o">.</span><span class="na">getTargetClass</span><span class="o">(</span><span class="n">handlerMethod</span><span class="o">.</span><span class="na">getBean</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>如上源码，这里用到了缓存。第一次执行时，会创建一个 ExceptionHandlerMethodResolver。</p>
<p>ExceptionHandlerMethodResolver 构造函数中，就会查找异常处理类中所有带有 @ExceptionHandler 的方法。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ExceptionHandlerMethodResolver</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">MethodFilter</span> <span class="n">EXCEPTION_HANDLER_METHODS</span> <span class="o">=</span> <span class="n">method</span> <span class="o">-&gt;</span>
</span></span><span class="line"><span class="cl">			<span class="n">AnnotatedElementUtils</span><span class="o">.</span><span class="na">hasAnnotation</span><span class="o">(</span><span class="n">method</span><span class="o">,</span> <span class="n">ExceptionHandler</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="nf">ExceptionHandlerMethodResolver</span><span class="o">(</span><span class="n">Class</span><span class="o">&lt;?&gt;</span> <span class="n">handlerType</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 使用反射查找处理类中的所有带有 @ExceptionHandler 注解的方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">for</span> <span class="o">(</span><span class="n">Method</span> <span class="n">method</span> <span class="o">:</span> <span class="n">MethodIntrospector</span><span class="o">.</span><span class="na">selectMethods</span><span class="o">(</span><span class="n">handlerType</span><span class="o">,</span> <span class="n">EXCEPTION_HANDLER_METHODS</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="n">Class</span><span class="o">&lt;?</span> <span class="kd">extends</span> <span class="n">Throwable</span><span class="o">&gt;</span> <span class="n">exceptionType</span> <span class="o">:</span> <span class="n">detectExceptionMappings</span><span class="o">(</span><span class="n">method</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">addExceptionMapping</span><span class="o">(</span><span class="n">exceptionType</span><span class="o">,</span> <span class="n">method</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>异常的处理逻辑源码：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ServletInvocableHandlerMethod</span> <span class="kd">extends</span> <span class="n">InvocableHandlerMethod</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">invokeAndHandle</span><span class="o">(</span><span class="n">ServletWebRequest</span> <span class="n">webRequest</span><span class="o">,</span> <span class="n">ModelAndViewContainer</span> <span class="n">mavContainer</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="n">Object</span><span class="o">...</span> <span class="n">providedArgs</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 重点：具体方法调用逻辑
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Object</span> <span class="n">returnValue</span> <span class="o">=</span> <span class="n">invokeForRequest</span><span class="o">(</span><span class="n">webRequest</span><span class="o">,</span> <span class="n">mavContainer</span><span class="o">,</span> <span class="n">providedArgs</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="c1">// TODO 使用返回值处理器，对返回值进行处理
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="k">this</span><span class="o">.</span><span class="na">returnValueHandlers</span><span class="o">.</span><span class="na">handleReturnValue</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">                <span class="n">returnValue</span><span class="o">,</span> <span class="n">getReturnValueType</span><span class="o">(</span><span class="n">returnValue</span><span class="o">),</span> <span class="n">mavContainer</span><span class="o">,</span> <span class="n">webRequest</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略部分代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>首先反射调用异常处理方法，然后调用返回值处理。</p>
<p>反射调用逻辑：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">InvocableHandlerMethod</span> <span class="kd">extends</span> <span class="n">HandlerMethod</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">Object</span> <span class="nf">invokeForRequest</span><span class="o">(</span><span class="n">NativeWebRequest</span> <span class="n">request</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">ModelAndViewContainer</span> <span class="n">mavContainer</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="n">Object</span><span class="o">...</span> <span class="n">providedArgs</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 重点：获取参数数组
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Object</span><span class="o">[]</span> <span class="n">args</span> <span class="o">=</span> <span class="n">getMethodArgumentValues</span><span class="o">(</span><span class="n">request</span><span class="o">,</span> <span class="n">mavContainer</span><span class="o">,</span> <span class="n">providedArgs</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 方法的反射执行
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="n">doInvoke</span><span class="o">(</span><span class="n">args</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>handleReturnValue() 中会处理返回值。比如有页面跳转、json数据流的响应，他们的处理方式是不一样的。通过策略模式，选择合适的处理类进行处理。</p>
<p>源码如下：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
</span><span class="lnt"> 2
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerMethodReturnValueHandlerComposite</span> <span class="kd">implements</span> <span class="n">HandlerMethodReturnValueHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kt">void</span> <span class="nf">handleReturnValue</span><span class="o">(</span><span class="nd">@Nullable</span> <span class="n">Object</span> <span class="n">returnValue</span><span class="o">,</span> <span class="n">MethodParameter</span> <span class="n">returnType</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="n">ModelAndViewContainer</span> <span class="n">mavContainer</span><span class="o">,</span> <span class="n">NativeWebRequest</span> <span class="n">webRequest</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">Exception</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 查找返回值处理器，策略模式的一种运用
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">HandlerMethodReturnValueHandler</span> <span class="n">handler</span> <span class="o">=</span> <span class="n">selectHandler</span><span class="o">(</span><span class="n">returnValue</span><span class="o">,</span> <span class="n">returnType</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 如果不存在返回值处理器，则跑出异常
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">handler</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">throw</span> <span class="k">new</span> <span class="n">IllegalArgumentException</span><span class="o">(</span><span class="s">&#34;Unknown return value type: &#34;</span> <span class="o">+</span> <span class="n">returnType</span><span class="o">.</span><span class="na">getParameterType</span><span class="o">().</span><span class="na">getName</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 对返回值进行处理
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">handler</span><span class="o">.</span><span class="na">handleReturnValue</span><span class="o">(</span><span class="n">returnValue</span><span class="o">,</span> <span class="n">returnType</span><span class="o">,</span> <span class="n">mavContainer</span><span class="o">,</span> <span class="n">webRequest</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>处理类的选择源码：</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre tabindex="0" class="chroma"><code><span class="lnt"> 1
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">HandlerMethodReturnValueHandlerComposite</span> <span class="kd">implements</span> <span class="n">HandlerMethodReturnValueHandler</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="n">HandlerMethodReturnValueHandler</span> <span class="nf">selectHandler</span><span class="o">(</span><span class="nd">@Nullable</span> <span class="n">Object</span> <span class="n">value</span><span class="o">,</span> <span class="n">MethodParameter</span> <span class="n">returnType</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="kt">boolean</span> <span class="n">isAsyncValue</span> <span class="o">=</span> <span class="n">isAsyncReturnValue</span><span class="o">(</span><span class="n">value</span><span class="o">,</span> <span class="n">returnType</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 遍历容器中所有的返回值处理器，判断是否支持，如果有返回值处理器支持这个返回值，则返回此处理器。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 这也是策略模式的一种运用。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">for</span> <span class="o">(</span><span class="n">HandlerMethodReturnValueHandler</span> <span class="n">handler</span> <span class="o">:</span> <span class="k">this</span><span class="o">.</span><span class="na">returnValueHandlers</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">isAsyncValue</span> <span class="o">&amp;&amp;</span> <span class="o">!(</span><span class="n">handler</span> <span class="k">instanceof</span> <span class="n">AsyncHandlerMethodReturnValueHandler</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">continue</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">handler</span><span class="o">.</span><span class="na">supportsReturnType</span><span class="o">(</span><span class="n">returnType</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="n">handler</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>              
</span></span></code></pre></td></tr></table>
</div>
</div><p>与之前流程中用到的策略模式，一样的套路。</p>
<p>判断是否支持处理对应的返回值，如果支持，就调用对应的 handleReturnValue()。</p></div>

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